This application claims the priority of Japanese application No. 9-030525, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a field pole position estimating method and means for estimating a field pole position of a synchronous motor, a motor controller for controlling a synchronous motor at the time of activation by using the field pole position estimating means, and an electric vehicle.
In controlling a synchronous motor, since the phase of an A/C voltage applied to a synchronous motor is determined by the present field pole position of a rotor, it is necessary to detect the accurate field pole position of the rotor. Although it can be detected during rotation by using an output signal of a rotation pulse generating means for detecting the speed, that is, an encoder or the like, the output signal of the encoder cannot be used at the time of activation. A dedicated field pole position detector is therefore provided to detect the field pole position at that time of activation, and the phase of a voltage command is determined by a detection value of the detector.
The field pole position detector is usually constructed by three pole position detectors for phases of U, V, and W. Since the pole position is detected by a combination of commands of the phases, a variation error in a range from +30.degree. to -30.degree. is included. In motor controllers, especially in a controller used for an electric vehicle, there is a problem of high costs due to the use of the detector exists. Further, there is the possibility that a required torque cannot be assured due to influences of the variation error at the time of activation. There are also control problems associated with the time of activation on a steep slope or the like, and when the field pole position detector itself is broken, or inoperative. A method of estimating the field pole position without using the dedicated detector is therefore considered to be effective in solving the above problems.
Japanese Patent Application Laid-Open No. (JP-A) 7-245981 discloses a conventional technique of a field pole position sensorless control of a synchronous motor. According to the technique, current vectors of parallel and orthogonal component, are detected with respect to a vector of an alternating voltage which is applied to a synchronous motor of a salient pole type the phase angle between the applied vector and the magnetic flux axis is calculated from at least one of the components and the field pole position is estimated from the obtained phase angle. According to the technique, since the alternating voltage is applied to the magnetic flux axis, the field pole position can be estimated without allowing the motor to generate a torque.
According to "Evaluation of Estimation Accuracy in Mechanical Sensor-less Rotor Position Detecting Method of Permanent Magnetic Motor using Current Vector Locus", literature No. 180 published in the national convention of The Industry Applications Society of The Institute of Electrical Engineers of Japan, 1995, in the case where the A/C voltage is applied to a synchronous motor of a salient pole type when the motor is stopped, the vector loci of the stationary coordinates .alpha..beta. axis currents draw an ellipsoid in which the magnetic flux axis or the d-axis direction is expanded. If the longitudinal axis direction is obtained, and correction is performed on the basis of the frequency, the field pole position can be detected.
The conventional techniques have, however, the following problems. According to the technique disclosed in JP-A-7-245981, where a voltage vector is applied to the d- and q-axes of the rotational coordinates which are set on a drive device side and a motor current that flows accordingly is detected and the field pole position is calculated. The arithmetic expression used in this case is based on the voltage current equation of the synchronous motor. When it is considered that the voltage current equation includes inductances Ld, Lq of the d- and q-axes which fluctuate due to change in currents id, iq of the d- and q-axes, deterioration of the detection accuracy occurs because of the parameter error. According to the technique disclosed in the literature No. 180, since the detection value is deviated from the actual value by an amount of the phase difference between the impedances of the d-axis and the q-axis, correction is necessary. The arithmetic expression for obtaining the correction amount also includes the inductances Ld, Lq, which fluctuate by the change in the currents id, iq as mentioned above, so that the detection accuracy is affected by the parameter error.
On the other hand, the detecting method using the field pole position detector is not worthless. Instead it is a valuable way to improve the method of field pole position detection. A synchronous motor of a salient pole type in which a reluctance torque can be used is often employed as a motor for driving an electric vehicle. It is therefore necessary to accurately detect a field pole position of the synchronous motor of the salient pole type. In addition, the subject of high reliability and low cost of the field pole position detector is also a subject of the controller for an electric vehicle which controls the synchronous motor an electric vehicle.
It is an object of the invention to provide a method of estimating a field pole of a synchronous motor accurately.
Another object of the invention is to provide a reliable and cheap motor controller and electric vehicle using a field pole position estimating means.
According to a feature of the invention, an alternating current signal is applied in the d-axis direction of rotational coordinates of a synchronous motor, and a field pole position estimation value of the synchronous motor is converged by using a feedback current signal in the q-axis direction of the rotational coordinates generated by the application of the signal. This facilitates the estimation of the field pole position of the synchronous motor.
According to another feature of the invention, an alternating current voltage command at an angular frequency, in a range where a reactance component each of impedances of both of the d-axis and q-axis of the rotational coordinates is larger than predetermined times of a resistance component, is applied to a synchronous motor. The field pole position of the synchronous motor is then estimated from a motor current flowed in response to the alternating current voltage command and a field pole position polarity of the synchronous motor.
According to yet another feature of the invention, in a motor controller for controlling a synchronous motor by using a field pole position estimation value generated by a field pole position estimating means which estimates the field pole position, the field pole position estimating means applies an alternating current signal in the d-axis direction of rotational coordinates of the synchronous motor. The field pole position estimating means also converges the field pole position estimation value by using a feedback current signal in the q-axis direction of the rotational coordinates generated in response to the application, and generates the resultant field pole position estimation value.
According to still another feature of the invention, the field pole position estimating means applies an alternating current voltage command at an angular frequency, in a range where a reactance component of each of impedances of the d- and q-axes of the rotational coordinates is larger than predetermined times of a resistance component to the synchronous motor, and generates the field pole position estimation value from a motor current flowed in response to the alternating current voltage command and a field pole position polarity of the synchronous motor.
According to another feature of the invention, in a motor controller comprising a synchronous motor, a power converter for supplying an alternating current power to the synchronous motor, a calculating means for generating an alternating current voltage command to the power converter to thereby control the synchronous motor, and a rotation pulse generating means for detecting the rotating position of the synchronous motor, the calculating means has a field pole position estimating means for estimating the field pole position of the synchronous motor. The synchronous motor is controlled by using a field pole position detection value generated by the rotation pulse generating means and a field pole position estimation value generated by the field pole position estimating means.
According to another feature of the invention, an electric vehicle is controlled by the motor controller.
According to the invention, since influences by factors of inductances Ld, Lq in the d- and q-axes directions are eliminated, the field pole position can be estimated with great accuracy. Further, since the field position detector can be made unnecessary by using the field pole position estimating means of the invention, a very reliable and accurate motor controller and controller for an electric vehicle can be provided at low costs.